Elastomeric polyurethanes are proposed in various product areas, for example as elastomeric films or elastomeric coatings, e.g. elastomeric film coatings. In recent years, superabsorbent polymer particles (SAP, or also referred to as absorbent gelling material, AGM) with elastomeric polyurethane coatings have been proposed. Such coated superabsorbent polymer particles (e.g. when incorporated in an absorbent structure or article) have been found to have a higher gel strength, whilst still having an excellent sorption capacity. (Together with other properties of the swollen polymer particles, gel strength relates to the tendency of the swollen polymer particles to resist deformation under an applied stress. The gel strength needs to be high enough in the absorbent member or article, to reduce deformation and to avoid that the capillary void spaces between the particles are filled to an unacceptable degree, causing so-called gel blocking. This gel blocking inhibits the rate of fluid uptake or the fluid distribution, i.e., once gel blocking occurs, it can substantially impede the distribution of fluids to relatively dry zones or regions in the absorbent article and leakage from the absorbent article can take place well before the water-swellable polymer particles are fully saturated or before the fluid can diffuse or wick past the “blocking” particles into the rest of the absorbent article.)
For example patent applications EP1651283-A and WO2006/083585 describe absorbent articles with superabsorbent polymer particles comprising coatings, e.g. film-coatings, of elastomeric polyurethanes that are extensible even when wet (e.g. when the particles are or have been absorbing fluid), having a high elongation to break, and that are furthermore hydrophilic, to allow sufficient aqueous liquid affinity and that are liquid permeable. Such proposed elastomeric polyurethane coatings can thus effectively extend upon swelling of the particles, and remain substantially complete coatings around the particle, and they can thus effectively reduce deformation of the coated, swollen particle, even when the coating is expanding and wet. Thus, such coatings help to ensure that such particles adopt more spherical shapes upon swelling and allowing more time for the fluid to diffuse through freely through the superabsorbent polymer particles in the absorbent article.
Polyurethane coating and/or films should have good mechanical integrity in terms of durability, in the dry state and preferably in wet state, including when handled in bulk quantities, and they should have a good resistance to tearing, both in dry state and preferably or more importantly in wet state, and they should have good initial elastomeric modulus, along with good propensity to elongate, in the wet state. Furthermore, in some instances, sufficient long term force relaxation may be beneficial, for example for helping to increase the capacity of the coated superabsorbent particles, by lowering the contractive forces on the particles over time.
There is still a need for even higher performance (including for example when wet) elastomeric polyurethane coatings or films in a variety of commercial applications, so that they may be applied in lower amounts and/or so that they may be used as thinner coatings or thinner films.